Conventionally, various kinds of methods are proposed and put into practice for generating ions in an ion beam generator. Contrary to the idea that almost all of methods are ones utilizing a discharge, ion sources utilizing laser lights have been recently developed. There are two ionizing methods utilizing laser lights. One of them uses plasma as an ion source which plasma are generated by irradiating lights, such as laser light, to solid material, such as metal, or by irradiating a bunching laser light to a gas or liquid material. The second method is one which ionizes the material by making a laser light of mono-wavelength resonate with the energy level of the material to be ionized using a variable wavelength laser. The present invention relates to this latter type of ion beam generator.